Method iter

include/pybind11/stl_bind.h:670–670

    explicit KeysViewImpl(Map &map) : map(map) {}
    size_t len() override { return map.size(); }
    iterator iter() override { return make_key_iterator(map.begin(), map.end()); }
    bool contains(const handle &k) override {
        try {
            return map.find(k.template cast<typename Map::key_type>()) != map.end();